Department of Radiology, University of California, San Diego, CA 92093, USA.

Abstract

Time perception emerges from an interaction among multiple processes that are normally intertwined. Therefore, a challenge has been to disentangle timekeeping from other processes. Though the striatum has been implicated in interval timing, it also modulates nontemporal processes such as working memory. To distinguish these processes, we separated neural activation associated with encoding, working-memory maintenance, and decision phases of a time-perception task. We also asked whether neuronal processing of duration (i.e., pure tone) was distinct from the processing of identity (i.e., pitch perception) or sensorimotor features (i.e., control task). Striatal activation was greater when encoding the duration than the pitch or basic sensory features, which did not differentially engage the striatum. During the maintenance phase, striatal activation was similar for duration and pitch but at baseline in the control task. In the decision phase, a stepwise reduction in striatal activation was found across the 3 tasks, with activation greatest in the timing task and weakest in the control task. Task-related striatal activations in different cognitive phases were distinguished from those of the supplementary motor area, inferior frontal gyrus, thalamus, frontoparietal cortices, and the cerebellum. Our results were consistent with a model in which timing emerges from context-dependent corticostriatal interactions.

Time and pitch discrimination task designs and performance. (a) Trial events, (b) Standard and comparison intervals for the time-discrimination task, (c) Standard and comparison frequencies for the pitch discrimination task, (d) Accuracy data from the time and pitch discrimination tasks, averaged across the 2 delay periods. Accuracy data were converted to the mean percent longer and percent higher for the time and pitch tasks, respectively. Data were averaged across the 3 SI/pitch tasks and their respective comparisons. For the time task, ± 1, 2, and 3 designate CIs that were approximately 9.2%, 17.5%, and 25% shorter (negative values) or longer (positive values) than the SI. For the pitch task, ±1, 2, and 3 designate comparison pitches that were approximately 0.92%, 1.35%, and 2% lower (negative values) or higher (positive values) than the standard pitch.

Time course of activation for the T, P, and C tasks in representative regions. Boxes along the x-axis indicate the time points selected in the short (10-s) delay condition to calculate the AUC for the encode (E: light gray), maintain (M: white) and decision (D: black) phases. Bracketed numbers refer to brain regions listed in and displayed in .

Results of the voxelwise ANOVA identifying regions showing significantly greater activation in the T or P tasks than the C task, or differing activation in the T versus the P task for the encode and maintenance phases. Numbers adjacent to activation foci correspond to numbers in .

Functional ROIs of the encode/maintenance conjunction map used to evaluate differences in MR signal intensity across the T, P, and C tasks. Numbers adjacent to activation foci correspond to numbers in .

Results of the voxelwise ANOVA identifying regions of significantly greater activation in the T or P tasks than the C task, or differing activation in the T versus the P task for the decision phase. Numbers adjacent to activation foci correspond to numbers in .